Acidic mucopolysaccharides such as hyaluronic acid or chondroitin sulfate have a high water retention, bond to collagen which serves as a column of intercellular substance matrix, and are mostly distributed in, for example, connective tissues, cartilaginous tissues and skin tissues, thereby being useful for keeping functions and forms of cells.
In the skin tissues, the acidic mucopolysaccharides, collagen, etc. mostly exist in corium layer and take a large part in water retention and resilience of skin. It is known that when the amounts thereof decrease due to aging or the like, the water retention and resilience of skin will be lost, thereby causing rough skin, fine wrinkles, etc.
Accordingly, in order to prevent and ameliorate the rough skin and fine wrinkles, it is important to maintain the moisture and tension of skin. For this purpose, cosmetics to which various components having effects for maintaining the moisture retention and resilience of skin are incorporated, are commercially available. As such components, for example, the mucopolysaccharides such as hyaluronic acid, chondroitin sulfate and collagen, low molecular weight saccharides such as trehalose and sorbitol, vitamins, amino acid derivatives, ceramide, α-orizanol, and fats and oils such as refined camellia oil, may be mentioned. Particularly recently, components derived from natural substances having a high safety are likely to be regarded as more worthy.
Further, many health and beauty care foods have been developed which enhance the above-mentioned effects by oral ingestion. For example, health and beauty care foods comprising nucleic acid and mucopolysaccharides which contain hyaluronic acid, chondroitin sulfate and collagen (Japanese Unexamined Patent Publication No. 10-165138), processed foods comprising as a main component a mixture of at least two food materials of active oxygen elimination factors, antiallergic factors, factors for improving e.g. skin, and antioxidation factors (Japanese Unexamined Patent Publication No. 10-70), foods comprising conchiolin or its processed product (Japanese Unexamined Patent Publication No. 8-173091), health foods comprising conjugated mucopolysaccharide wherein a mucopolysaccharide and peptide are bonded (Japanese Unexamined Patent Publication No. 9-98739), and health foods containing ceramide (Japanese Unexamined Patent Publication No. 11-113530), may be mentioned.
On the other hand, natural-type N-acetylglucosamine is one of natural aminosugars obtainable by decomposing a high molecular weight polysaccharide chitin contained in shells of crustacea such as crab and shrimp or lobster, and is a white crystalline powder having a good sweetness of about a half of sugar and being less in moisture absorption. Natural-type N-acetylglucosamine is also contained in milk in a free state in an amount of about 10 mg/100 ml, and exists universally in living organisms as constituting units of sugar chains of mucopolysaccharide, glycoprotein and glucolipide. Natural-type N-acetylglucosamine is usually produced from glucose as a starting material by metabolism in living organisms, and one of living organism components having a high safety to human being. As physiological actions of natural-type N-acetylglucosamine, amelioration of arthritis symptom, propagation-accelerating effect of Lactobacillus vifidus, and the like, have been known.
However, since hyaluronic acid, chondroitin sulfate, collagen and the like are high molecular weight compounds and hardly absorbed only by coating them on the skin like cosmetics, these components are used for the purpose of improving the water retention of skin surface when these are used for cosmetics. This is true for most of the above-mentioned other components. Further, if the high molecular weight compounds such as hyaluronic acid, chondroitin sulfate and collagen, are orally ingested, there is a problem in digestion and absorption and their effects are not necessarily satisfactory.